Electron discharge device of the cavity resonator type



H. R. HEGBAR Nov. 22, 1949 ELECTRON DISCHARGE DEVICE OF THE CAVITYRESONATOR TYPE Filed Nov. 17I 1943 nw@ nu nD amc mh MR mD R b Hum 'lATTRNEY Nov. 22, 1949 H. R. HEGBAR ELECTRON DISCHARGE DEVICE OF THECAVITY RESONATOR TYPE 2 Sheets-Sheet 2 Filed NOV. 17, 1943 INVENTORHwnRD RHEGBHR Mw ATTORNEY Patented Nov. 22, 1949 ELECTRON DISCHARGEDEVICE OF THE CAVITY RESONATOR TYPE Howard R. Hegbar, Princeton, N. J.,assignor to Radio Corporation of America, a corporation of DelawareApplication November 17, 1943, Serial No. 510,604

9 Claims. (Cl. 315-39) My invention relates to electron dischargedevices and associated circuits useful at ultra high frequencies andmore particularly to magnetrons and output leads to be used therewith.

In certain types of magnetrons the anode segments or elements areinterconnected by means of cavity resonator circuits and form togetherthe anode structure for the magnetron. In one form of magnetron theelectrode assembly comprises an elongated centrally positioned cathodeand an anode member surrounding the cathode and provided` with aplurality of cavity resonator circuits formed by cavities in the anodemember and having communicating passages or Slots between the cavitiesand the space between the cathode and anode member. The anode seg mentsare formed by portions of the anode member positioned between adjacentcommunicating passageways, for example the slots lying parallel to thecathode. The anode structure may, of course, be made in various ways,either by utilizing a ring supporting inwardly and radially directedvanes or the anode assembly may be breached from a solid block or may bemade by means of stacked sheets provided with proper slots andapertures.

In the usual multi-cavity magnetron of the type described, the outputlead for coupling the device to an output lead comprises a coaxial line.Such output leads can be coupled to the magnetron resonators by means ofa coupling loop placed in either a resonant cavity or in the magnetronend space adjacent the cavity resonators.

For a given length of coaxial output lead, measured from the output leadtermination to the junction of the coupling loop and output lead, thereis a certain size coupling loop which will permit the magnetron to workinto a proper impedance for maximum power output. This assumes somefixed standing wave ratio in the waveguide system; that is, it assumessome fixed ratio between the maximum and minimum voltages of thestanding waves in the system. It is advantageous that this standing waveratio be near unity. In magnetron construction it is difficult to buildtubes having output leads and coupling loops with identical electricalcharacteristics.

There are two general types of terminations used for magnetron coaxialoutput leads. One type has the center lead sealed through an insulatingseal, preferably glass, and the other type has the center lead entirelywithin the wall of the evacuated container which may include theenvelope or an extension from the envelope. This latter type may betermed the antenna termination. It is known that such output leadsinserted in waveguides have the disadvantage of having corona form insome region adjacent the coaxial termination when operated at high powerlevels. Such corona forms at the coaxial output lead termination atpower levels well below that at which the connected waveguide systemcould operate corona-free.

It is an object of my invention to provide an electron discharge deviceof the magnetron type having improved means for coupling the magnetronto a load.

It is a further object of my invention to provide an electron dischargedevice of the magnetron type, particularly of the cavity resonator typein which the output lead for diierent magnetrons have substantiallyidentical electrical characteristics.

It is a further object of my invention to provide an output lead for acavity resonator magnetron which is simple in construction and which iscapable of accurate reproduction and which can be easily made.

A still further object of my invention is to provide an output leadwhich will operate at power levels above those normally associated withconventional output leads.

A still further specic object of my invention is to provide output leadswhich will eliminate the necessity for employing loops and seals forcoaxial line type coupling arrangements.

The novel features which I believe to be characteristic of my inventionare set forth with particularity in the appended claims, but theinvention itself will best be understood by reference to the followingdescription taken in connection with the accompanying drawing in whichFigure 1 is a longitudinal section of one form of an electron dischargedevice and an output lead made according to my invention, Figure 2 is alongitudinal section taken at to Figure l, Figure 3 is a transversesection taken along the line 3-3 of Figure l, Figure 4 is a perspectiveview showing the coupling arrangement between a waveguide and the outputlead disclosed in Figures 1, 2 and 3, Figure 5 shows a modiiication ofan electron discharge device and output lead made according to myinvention, Figure 6 is a longitudinal section taken along the line t-Eof Figure 5, and Figure '7 is a section taken along the line 'I-l ofFigure 6, Figure 8 is a perspective of another method of coupling theoutput lead made according to my invention to a waveguide;

Referring to Figure 1, the magnetron employs a metallic evacuatedenvelope Ill of rectangular transverse section containing a magnetronmount assembly which includes preferably an indirectly heated cathode IIsurrounded by and coaxial with the anode assembly comprised of a heavyring member I 2 and the radially positioned vanes lying parallel tocathode, which form between the vanes I3 cavity resonators of more orless U-shape. These vanes I3 are connected together by means ofring-like straps I4 and I5 which engage alternate vanes to insure aproper mode of operation. The cathode is heated by means of the heaterII' and an electron shield II at the top of the assembly. Cathode heaterleads IS and I'I are shielded from the anode assembly by means of theshield I8, the cathode heater assembly and leads being supported bymeans of the tubular member I9 and bracket 2G supported from the anodeassembly and the insulating supporting member 2|, preferably of glass.The cathode heater leads extend through the tubular shield member 22 andare sealed vacuum-tight by means of the insulating cup-shaped member 23.The envelope may be exhausted through the tubular member 24 which istipped-off after evacuation.

In accordance with my invention the anode assembly has a portion removedfrom one side thereof and a coupling perforation extending normal to thecathode so as to provide communication from one resonator between twovanes to the exterior of the anode assembly. The envelope It is alsoprovided with a registering coupling aperture 24. In accordance with myinvention I provide an output lead which includes a tubular memberhaving an elongated rectangular transverse section, the first section 25of which is also provided with a coupling aperture 24 registering withthe apertures in the anode assembly and in the wall of the casing. Thismember 25 is in turn received with a second rectangular tubular member26, the other end of which is sealed vacuum-tight by means of closuremember 21 permeable to electromagnetic waves. The end sealed of thismember 26 is in turn coupled to the end of waveguide member 28 andinsulated therefrom by member 29. A quarter wave overlap is employed sothat minimum impedance Vis provided for any R.F. current inside thewaveguide. A magnetic eld for the magnetron is provided by magnets 60and 6I.

It will be observed that the waveguide 28 is so oriented with respect tothe anode that so-called Ho,1 wave is generated within the output lead,the longer axis of the guide lying parallel to the cathode. Inasmuch ascirculating currents flow in the walls of the cavity resonator such thatthe magnetic lines of force are parallel to the cathode, these magneticlines extend through coupling aperture 24, 24', 24 to excite the outputlead and coupled waveguide. This is the simplest coni-iguration` of anyrectangular hollow tube wave. With this arrangement radiation from thewaveguide will be most effective. This feature is unique to the Ho,1wave and rectangular hollow tube and makes it especially adaptable as aradiator.

The Ho,1 is also referred to as the IEo1 mode of wave propagationthrough waveguides. In this mode of propagation, the electric field istransverse to the propagation and has no component along the axis ofpropagation. The magnetic iield lies parallel to the direction ofpropagation and has no component transverse to the direction ofpropagation. In other words, the mag- 4 netic eld lies along the axis ofthe tube. In this form of wave the electric ield has one peak having amaximum intermediate the short ends of the waveguide.

In Figures 5 to '7, inclusive, is shown a diierent type of magnetronwith a modification of an output lead made according to my invention. Asshown in Figures 5 andd, the indirectly heated cathode 3d is surroundedby a laminated anode assembly comprising a plurality of stacked punchedlplates 3|, 32, 33 and 34, these plates being so punched that aplurality of radially directed slots of substantially uniform width areprovided in the anode structure. These slots act as cavity resonatorswith the inner ends of the lingers acting as anode segments. Top andbottom cup-shaped members 35 and til are closed by means of telescopedcup-shaped members 42 and i3 to provide a vacu-lnnfor the electrodeswithin the envelope so provided, the plates being vacuum sealed by meansof, for example, silver solder between the plates. The cathode assemblyis supported within the anode assembly by means of the brackets 'i and4I supporting the bridge 37 by means of the insulating U-shaped elements33 and 39. Electromagnets 4l and i8 are inserted within the cup-shapedmember to provide the magnetic elds. As shown in Figure 5 the cathodeheater is supplied by means of cathode heater leads i4 and 45 sealed inthe envelope by means of insulating cup-shaped element 45.

In accordance with my invention one of the slots is coupled to theoutput lead by a ilared coupling opening or chamber 4S extending fromthe outer end of the slot to the outer wall of the anode assembly. Thecoupling chamber de receives the tubular waveguide output lead 5G, whichmay be of rectangular shape and vacuum sealed by means of the windowclosure 5I permeable to electromagnetic Wave. The coupling chamberserves as a transition device for matching the impedance of themagnetron slot to that of the output lead. As in the case shown inFigure l, Hm waves are generated which travel down along the waveguideoutput lead 5) with maximum efliciency. In the arrangement shown in Fig.8, the wave guide 55, which may be the one directly coupled to themagnetron through the aperture, is coupled to a second Wave guide 55,the wave guides being provided with lips 5l and 58. Each of the lips isa quarter Wave length wide at the operating frequency and extendstransversely of the wave guide. The high impedance at the outer edges ofthe lips produces a low impedance at the inner edges of the lips whichminimizes leakage from the wave of high frequency energy passing throughthe wave guides.

The output leads may be made of any suitable metal, or combination ofmetals. In particular, Such a suitable combination of metals as Kovarand copper may be used. The surfaces of the leads may be plated toincrease the electrical conductivity. Other shapes of cavity quarterwave joints may be used to connect output leads to waveguide systems.

The coupling perforation described permits accurate reproduction-andmakes possible the manufacture of magnetrons` having nearly identicaloperating characteristics. Perforations may be punched or drilled tocloser tolerances than loops and coaxial lines may be fabricated. Thusonly very small tuning changes are required in the waveguide system whenmagnetrons are interchanged.

The output lead and termination have no regions in air 'in whichexcessive electrical intensities are produced relative to those in thewaveguide system. Thus, this combination may be used at higher powerlevels with no corona.

While I have indicated the preferred embodiments of my invention ofwhich I am now aware and have also indicated only one specic applicationfor which my invention may be employed, it will be apparent that myinvention is by no means limited to the exact forms illustrated or theuse indicated, but that many variations may be made in the particularstructure used and the purpose for which it is employed withoutdeparting from the scope of my invention as set forth in the appendedclaims.

What I claim as new is:

1. An apparatus for use at high radio frequencies, including a cavityresonator, means for providing an electron discharge for exciting saidresonator, said resonator having an aperture extending through a wallthereof, and a waveguide adjacent said resonator and having an apertureopening into the aperture in said resonator, said wave guide comprisingan elongated hollow tubular member having its end remote from theapertured wall sealed by a closure member permeable to electromagneticwaves, said waveguide having a rectangular shaped transverse section andbeing oriented with respect to said cavity resonator so that Hui typeelectromagnetic waves are developed within the waveguide.

2. An electron discharge device having an envelope of elongatedflattened rectangular shaped transverse section, an electrode assemblywithin said envelope and including a cathode surrounded by an anodemeans having a plurality of cavity resonators, the longitudinal axis ofsaid cathode and anode means lying parallel to the shorter axis of saidenvelope, said anode means having one side abutting one end of the wallof said envelope, said anode means having an aperture extendingtherethrough and opening into one of said resonators, said envelopehaving an aperture registering with the aperture in said anode means anda waveguide extending from and secured to said envelope and having anaperture registering with the apertures in said envelope and said anodemeans, said waveguide having a rectangular transverse section the longeraxis of which lies parallel to the longitudinal axis of said cathode,said waveguide having the end remote from said envelope closed by meanspermeable to electromagnetic waves.

3. An electron discharge device having a metal elongated envelope ofrectangular-shaped transverse section, an electrode assembly mountedwithin said envelope and including a cathode lying parallel to theshorter axis of said rectangular envelope, an anode assembly surroundingsaid cathode, said anode assembly having a plurality of cavityresonators opening into the space surrounding said cathode, said anodeassembly being flattened and having its shorter axis parallel to theshorter axis of said envelope, said anode assembly contacting one end ofsaid envelope, the end of said envelope and said anode assembly havingregistering apertures opening into one of said resonators, and awaveguide supported by one end of said envelope and having aperturesopening into the aperture in said envelope and said anode assembly, saidwaveguide having a rectangular-shaped transverse section, the longeraxis of said waveguide lying parallel to said cathode, and meanspermeable to electromagnetic waves closing the end of said waveguideremote from said envelope.

4. An electron discharge device having an envelope of flattenedrectangular shaped transverse section, an electrode mount assemblywithin said envelope and including an elongated cathode surrounded by ananode block including a plurality of cavity resonators, the interior ofsaid envelope communicating with the space between the cathode and theanode block, said anode block having a passageway extending therethroughand opening into the interior of one of said cavity resonators, saidelectrode assembly being adjacent one end wall of said envelope, saidend wall of said envelope having an aperture opening into the aperturein said anode block, and a hollow waveguide having an elongatedtransverse section and extending from an outside wall of said envelopeand communicating with the apertures in the wall of said envelope andsaid anode block, the longer transverse axis of said waveguide lyingparallel to the axis of said cathode.

5. An electron discharge device including a cathode and an anode blockhaving a central chamber, said cathode being within said chamber, saidanode block having a plurality of radially-extending slots ofsubstantially uniform width communicating with the chamber between thecathode and the anode block and forming resonators, the end of one ofsaid slots remote from said cathode opening into a coupling chamberhaving side walls diverging toward the outside of said anode block, anda tubular output lead extending from said block and opening into saidcoupling chamber, said tubular output lead having a rectangular shapedtransverse section and being oriented with respect to said one slot andcoupling chamber so that Ho,1 type electromagnetic waves are developedwithin the output lead.

6. An electron discharge device including an anode block, said anodeblock being provided with a central chamber and having a plurality ofradially extending slots of substantially uniform width communicatingwith said chamber, and a cathode mounted within said chamber, the end ofone of said slots remote from said cathode opening into a couplingchamber having side walls diverging toward the outside of said anodeblock, a tubular output lead extending from said block and having oneend opening into said coupling chamber and having its other end sealedby a closure member permeable to electromagnetic waves said tubularoutput lead having a rectangular shaped transverse section and beingoriented with respect to said one slot and coupling chamber so that Haitype electromagnetic waves are developed within the output lead, andmeans for providing a magnetic field between said cathode and anodeblock.

7. An electron discharge device comprising an electrode assemblyincluding an indirectly heated cathode, an anode assembly coaxial withand surrounding said cathode, said anode assembly including a pluralityof laminations having radially extending slots of substantially uniformwidth registering with each other, one group of registering slotsopening into a coupling chamber having an increasing transverse sectionmoving from the inside to the outside of said anode assembly, saidchamber opening into a hollow output lead of rectangular section havingits longer axis parallel to the longitudinal axis of the cathode,closure members for the ends of said electrode assembly for providing anevacuated space for the electrode assembly and means for providing amagnetic field between said cathode and anode block and parallel to saidcathode.

8. An electron discharge device comprising an electrode assemblyincluding an indirectly heated cathode, an anode assembly coaxial withand surrounding said cathode, said anode assembly including a pluralityof laminations having radially extending slots of substantially uniformwidth registering with each other, one group of registering slotsopening into a coupling chamber having an increasing transverse sectionmoving from the inside to the outside of said anode assembly, anelongated tubular output lead having one end opening into said chamber,closure members for the ends of said electrode assembly for providing anevacuated space for the electrode assembly, means for providing amagnetic iield between said cathode and anode block and parallel to saidcathode, and a closure member permeable to electromagnetic waves andsealing the said other end of said tubular output lead.

9. An apparatus for use at high radio frequencies, including a cavityresonator, means for providing an electron discharge for exciting saidresonator, said resonator having an aperture extending through a wallthereof, and a hollow wave guide extending outwardly from the outsidewall of said resonator and opening into the aperture in said resonator,said wave guide Comprising an elongated tubular member having its endremote from the apertured wall of said resonator sealed by an insulatingmedium permeable REFERENCES CITED The following references are of recordin the le of this patent:

UNITED STATES PATENTS Number Name Date 1,684,947 Daumann Sept. 18, 19282,063,342 Samuel Dec. 8, 1936 2,200,023 Dallenbach May 7, 1940 2,223,082Van Mierlo Nov. 26, 1940 2,247,077 Blewett et a1 June 24, 1941 2,283,935King May 26, 1942 2,298,949 Litton Oct. 13, 1942 2,351,744 Chevigny June20, 1944 2,372,193 Fisk Mar. 27, 1945 2,402,184 Samuel June 18, 19462,404,086 Okress et al. July 16, 1946 2,408,409 Bowen Oct. 1, 19462,408,903 Biggs et al Oct. 8, 1946 2,446,825 Gurewitsch Aug. 10, 19482,450,023 Spencer Sept. 28, 1948 FOREIGN PATENTS Number Country Date215,600 Switzerland Oct. 16, 1941

